Searching for Alien Life? Try Failed Stars

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The search for alien life usually focuses on planets around other
stars. But a lesser-known possibility is that life has sprung up
on planets that somehow were ejected from their original solar
systems and became free-floating in the universe, as well as on
small bodies called sub-brown dwarfs, which are stars so small
and dim they are not really stars at all, but function more like
planets.

Studies show these bodies could potentially host atmospheres and
surfaces where some form of
extraterrestrial life could take hold.

Researcher Viorel Badescu of the Polytechnic University of
Bucharest in Romania recently investigated the possibilities for
life on free-floating planets (FFPs) and sub-brown dwarfs (SBDs)
that might contain lakes
of the chemical ethane. He found that such life is not
impossible, though it would be significantly different from life
on Earth.

His findings were detailed in the August 2010 issue of the
journal Planetary and Space Science.

Failed stars

Sub-brown dwarfs are not large enough to generate the nuclear
fusion that powers normal stars. Having
failed as stars, they slowly radiate their internal thermal
energy as heat and very dim light – hence, they are extremely
hard to detect. Both free-floating planets and sub-brown dwarfs
don't always orbit around a parent star, and can be found in
interstellar space.

Lacking a star, life on FFPs and SBDs would have to rely on the
body's internal heat and the decay of radioactive elements for
energy. "One may expect a rather stable heat release for long
periods of time, exceeding two or three times the present age of
the solar system," said Badescu. Though meager, this heat could
be trapped on the object by an optically thick atmosphere.

But life needs more than just heat to thrive. Another important
ingredient for habitability is a solvent – a liquid environment
where important chemical reactions can occur. Life on Earth uses
water as a solvent, but that's not the only option.

"Synthesis of observational data makes it possible to conceive
chemical reactions that might support life involving non-carbon
compounds, occurring in solvents other than water," Badescu wrote
in his paper.

In particular, Badescu found that ethane – a compound of carbon
and hydrogen – could function well as a solvent for alien life.
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Life without water

It seems odd to consider the possibility of life on an object
more massive than Jupiter or Saturn, especially since most
scientists think such gas giant planets -- with their high
radiation, hostile atmospheres and potential lack of a planetary
surface -- would not harbor life as we know it.

The main difference between water and ethane for use as a solvent
is that water is a polar molecule, meaning one end of the
molecule is positively charged, and one end of it is negatively
charged. This has proven integral to Earth life, because the
polar properties of water enable certain kinds of molecules to
dissolve easily in water, while others remain stable.

The molecules that code for life – DNA and RNA – have electrical
charge properties that allow them to change their internal
structure – the specific order of the base molecules within them
– and still have the same overall physical properties. This is
all enabled by the way their charge properties interact with the
polar quality of water.

That would not be the case with ethane, which is a non-polar
molecule. With DNA and RNA in this situation, "small changes in
molecular structure may create large changes in molecular
behavior," Badescu said. "That is not acceptable in an encoding
biopolymer that must support Darwinian evolution, in which case,
the molecule's physical properties must remain relatively
constant when the informational content changes."

However, the challenge is not insurmountable – a completely
different type of molecule could be used to code life's blueprint
on a FFP or SBD.

Searching for life

Ultimately, free-floating planets and sub-brown dwarfs could
prove a fertile place to look for extraterrestrial creatures.

Besides their habitable qualities, these bodies seem to be quite
common in the universe. Sub-brown dwarfs weighing between 1 and
13 Jupiter masses may be about as common as stars, Badescu said.

"The total number of FFPs and SBDs may exceed the number of stars
by two orders of magnitude, although most of them should be
low-mass rock/ice planetary embryos ejected from planetary
systems in formation," i.e. not the type with large gaseous
atmospheres that would retain the heat required for life, Badescu
said. "Thus, it might be conceivable that FFPs and SBDs are the
most common sites of life in the universe."

Given this fact, he advocated ramping up our efforts to search
for
free-floating planets and sub-brown dwarfs and to
characterize them to determine which might be habitable.

"Present day technology does not allow a systematic search for
habitable FFPs and SBDs," Badescu said. "However, the existing
observation programs of young star forming regions should be
supplemented with activities related to FFP and SBD
identification and characterization."